GAS AND SOLUTION-PHASE NMR-STUDIES OF N-ETHYLMORPHOLINE INTRAMOLECULAR AND INTERMOLECULAR EFFECTS ON RING INVERSION RATE CONSTANTS

Temperature dependent gas phase H-1 NMR spectra of N-ethylmorpholine a re consistent with the following activation parameters for the ring in version process: DELTAG(double dagger) = 47.7 (0.3) kJ mol-1, DELTAH(d ouble dagger) = 47.1 (2.3) kJ mol-1, DELTAS(double dagger) - 1.9(4.9) J mol-1 K-1, E(act) = 49.2(2.3) kJ mol-1 and A(infinity) = 1.2(0.4) x 10(13) S-1. Rate constants in the gas phase and in CDCl3 Solution are very similar while those obtained in CS2 solutions are almost twice as large at corresponding temperatures. Rate constants obtained for a 1% solution of N-methylmorpholine in CDCl3. obtained in the present stud y and those previously obtained in the gas phase and CS2 solutions sho w a similar trend. The observed phase and solvent dependent rate const ants do not agree with predictions based on simple steric or dielectri c considerations and may indicate that complex static and dynamic solv ent effects are important in the liquid solutions.